Abstract

Electron optical properties of nanometer diameter field emissionelectron sources have been calculated using ray tracing methods. The spherical and chromatic aberration coefficients referred to the object plane were found to be on the order of angstroms. The effective source size was estimated to be much smaller than that in a conventional field emission source. The ultimate resolution of a lensless point projection electron microscope, which depends on both the source aberrations and the effective source size, were also in the order of angstroms. The beam angular half‐width on the anode was 7.4° relative to the virtual image position on the optic axis, and the corresponding coherence width was 9.6°, suggesting that the source is totally coherent.